1. Field of the Invention
The present invention relates to a chain saw.
2. Description of Related Art
According to a traditionally known arrangement of a portable work machine such as a chain saw, a cooling fan provided adjacent to a first end of a crankshaft conveys cooling air to a cylinder for cooling the cylinder (for instance, document 1: JP-A-2001-355446).
In the portable work machine according to the document 1, a cooling fan (a blade wheel of an air blower) includes a hub (a partition) and cooling vanes (an intake blade ring body) projected respectively from an inward side of the hub (a side opposed to the crankcase) and an outward side of the hub (a side not opposed to the crankcase). In addition, a case cover (a machine case) is provided with: a first outer-air intake (a first inflow opening) in direct communication with the outside of the portable work machine for feeding outer air to the outward side of the cooling fan; and a second outer-air intake (a second cooling-air inlet) in communication with the outside through an outer-air inlet (a second inflow opening) for feeding outer air to the inward side of the cooling fan.
According to such a portable work machine as disclosed in the document 1, even when a first one of the outer-air intakes is clogged by a large amount of dust and the like generated during operations (including when the outer-air inlet is clogged as far as the second outer-air intake is concerned), the cooling vanes adjacent to a second one (i.e., non-clogged one) of the outer-air intakes can breathe through the second one of the outer-air intakes. Thus, cooling air can be reliably conveyed to the cylinder.
However, according to the portable work machine of the document 1, only the cooling vanes adjacent to the non-clogged outer-air intake can breathe. Thus, when the first one of the outer-air intakes is clogged, only the cooling vanes adjacent to the second non-clogged one of the outer-air intakes breathes for conveying the air, so that air flow conveyed to the cylinder is reduced.